Mixed Spinel Ni–Co Oxides: An Efficient Bifunctional Oxygen Electrocatalyst for Sustainable Energy Application

Ni–Co oxides with varying Ni:Co ratios have been synthesized following a facile sol–gel procedure. The influence of variation in composition on the electrocatalytic activity of Ni–Co oxides (Ni:Co = 1:1, 1:2, 1:3, and 1:4) for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is explored in high-pH media. The lattice structure, size, morphology, and surface composition of the synthesized nanocatalysts have been carefully verified by using X-ray diffraction and various microscopic and spectroscopic techniques. Among the synthesized catalysts, the Ni–Co oxide with Ni:Co = 1:3 exhibits the best electrochemical performance with onset potentials of 0.86 and 1.51 V for ORR and OER, respectively. Furthermore, it demonstrates a small potential difference (0.82 V) between the potential corresponding to 10 mA cm–2 current density for OER and the half-wave potential for ORR. The catalyst exhibits admirable catalytic capability, almost comparable to that of the benchmark Pt/C catalyst and rivalling that of the IrO2/C catalyst for OER. This work shed light on the development of a highly active non-precious metal-based energy conversion catalyst and the effect of variation of compositional ratios on the electro-catalytic performance, which will further help rationally design efficient electrocatalysts for sustainable energy applications.